Synthetic ligament for the knee

ABSTRACT

A synthetic ligament for knees, made of biocompatible material, including an active ligamentary part arranged between the femoral and tibial regions of intra-articular penetration. The active ligamentary part having a first pair of parallel main elements and a second pair of intermediate elements which are crossed and integral with the first pair of main elements at the region of intra-articular penetration of the knee joint.

The present invention relates to a new type of synthetic ligamentparticularly designed for replacing the anterior cruciate ligament ofthe knee.

The anterior cruciate ligament of the knee joins the intercondylar areaof the tibia to the intercondylar fossa of the femur. Its principal roleis to check the forward slipping of the tibia, that is to say, to reducethe anterior drawer movements.

Orthopedic surgery of the knee has progressed greatly in recent yearsand there is an increasing tendency to offer ligament replacementprostheses.

Replacement prostheses for the anterior cruciate ligament in the kneeproposed heretofore consist of a single bundle of synthetic fibers orgroups of synthetic fibers which all terminate at one and the same siteat each of the ends of the bundle. This prosthesis makes it possible toreplace the anterior cruciate ligament and to limit the anteriordisplacement of the tibia under the femur created by the connection ofthe ligament to be replaced.

However, this system with a single bundle of fibers or groups of fiberslimits this drawer movement only at certain degrees of flexion. Ineffect, a single bundle of fibers does not provide isometric tension ofthe synthetic ligament at every degree of flexion, i.e., tension withoutshortening the ligament. Such a ligament is described in one of theembodiments of a surgical instrument designed for placement on thejoints of such ligaments in French Patent Application A 2 2598 311. Thisligament is single-stranded and, when placed in the joint, goes througha simple back-and-forth movement from the anterointerior surface of thetibia around a point of anchorage in the femur. In this way, as a resultof the independence of the forward-moving strand in relation to thereturn strand, stresses are never transmitted from one strand to theother, which reduces the resistance of the strand under stress and henceits useful life. In addition, this ligament, such as described, in noway prevents the anterior drawer movements of the tibia under the femur.

In point of fact, the inability of a single-stranded ligament to limitthe anterior drawer movements of the tibia under the femur is inherentin the variation of the radii of curvature of the femoral condyles atthe lower end of the femur, the condyles being in contact with the tibiain the glenoid cavity. These radii vary from front to back, alsoproducing a front-to-back displacement of the instant flexion-rotationcenters of the knee during flexion. Put differently, because of thepresence of the femoral condyles with variable curvature radii and alsobecause of the nonphysiological elasticity of these synthetic ligaments,continuous isometric tension of such a single-stranded ligament cannotbe achieved.

It was then proposed to resort to two single-stranded ligaments toovercome this overwhelming drawback. U.S. Pat. No. 4,411,027 describes apatellar suture material made from two individual strands. Actually, ituses not one, but two, suture materials. These two materials are placedahead of the knee joint by the classic "bracing" technique, which meansthat one of the suture materials simply goes around two points ofsupport placed, respectively, on the quadriceps tendon (at the lower endof the anterior muscle of the thigh also known as the quadriceps) and onthe tibia, and describes an oval, and the other one, also attachedthrough the two points of support mentioned above, describes an 8. Tothis day, this technique is well known in connection with patellartendon repair. However, it has some considerable disadvantages. First ofall, the fact that several suture materials are used means that, whenthe joint is working, one of the strands slides in relation to theother, and as a result produces friction. This is certainly favorablefor the healing of the patellar tendon, but causes premature andredhibitory wear of the strands as they pass through the tendon and thetibia, and in no way permits them to act as a prosthetic device. Next,as in the previous case, because the two strands are independent, thestresses are never transmitted from one strand to the other, which thenreduces the resistance of the strand under stress and thus affects itsuseful life. In addition, in order to make it possible to attach the twostrands to the joint, it is necessary to hollow out relatively largetunnels in the bone and tendon concerned to permit the passage of thetwo strands, thus weakening the former. Finally, if it is desired toapply the teachings of this document to the replacement of the anteriorcruciate ligament of the knee, the fact that the two strands are notintegral and the sliding in the insertion tunnels would mean that, whenthe joint is working, permanent tension of the prosthesis could not beachieved at every degree of flexion-rotation. In fact, it should benoted that this document does not claim a ligament prosthesis, butrather an absorbable suture material in connection with patellar tendonrepair, so that the application and purpose are different.

The object of the present invention is to overcome these disadvantages.It proposes a prosthesis for a synthetic ligament for the knee jointmade of biocompatible material comprising an active part of the ligamentplaced between the femoral and tibial intra-articular penetration areas,defining the entrances of tunnels made in the femur and in the tibia,respectively, and from the exit of which emerge the ends of theligament, the ends forming ties to be attached to the femur and thetibia, respectively.

It is characterized in that the active part of the ligament comprises:

a first set of two principal elements that are substantially parallel,extended by the ties, integral with each other at the level of theactive part of the ligament, as well as

a second set of two intermediate elements that are crossed at the levelof the active part of the ligament and integral with the first set ofprincipal elements starting from, and at the level of, the femoral andtibial intra-articular peneration areas, in the direction of the exit ofthe tunnels.

In other words, the present invention relates to a prosthesis for asynthetic cruciate ligament of the knee, consisting of two independentbundles of synthetic fibers of groups of fibers, each ending in an uppercondyle and lower glenoid (tibial) end, independent from each other,integral with two groups of fibers of the same kind, connecting theindependent bundles with each other. Put differently, the ligamentproposed in the present invention is he multistrand type, butconstitutes only a single entity.

Advantageously, in practice:

the femoral insertion areas of the principal elements are different;

the ligament is made of a one-piece textile material;

the first and second sets second sets of elements are made of abiocompatible knit textile material, and the second set of intermediateelement emerges from the first set of principal elements in the vicinityof the femoral and tibial intra-articular penetration areas;

the interlocking areas of the principal elements at the level of theactive part of the ligament are constructed by means selected from amongthe group consisting of braiding, knitting, welding and sewing;

the biocompatible textile material is a monofilamentous ormultifilamentous material selected from the group consisting ofpolyesters, polypropylene and glass;

the intermediate elements are made integral with the principal elementsby welding and, in particular, by heat sealing;

the ends of the ligament forming ties designed to be attached to thetibia and the femur are covered with a polyethylene sheath provided witha needle eye aperture to enable passage of ends in the tunnels.

The manner in which the invention can be implemented and the resultingadvantages will be better understood from the consideration of theensuing embodiment offered solely by way of non-limiting example andfrom the attached drawings, in which:

FIG. 1 is a schematic plane representation of a prosthesis according tothe invention,

FIG. 2 is a schematic lateral representation of the joint of the rightknee from which the internal condyle has been removed, showing thefemoral and tibial intra-articular openings for attaching theprostheses, which have been made in the anatomic insertion surfaces ofthe anterior cruciate ligament.

FIG. 3 is a schematic lateral representation of the joint of a rightknee in complete extension, the internal condyle of which has beenremoved and on which the prosthesis according to the invention is inplace.

FIG. 4 is a view similar to FIG. 3, but in which the joint is inflexion.

FIG. 5 is a view similar to FIGS. 3 and 4 in which the joint is in anintermediate position in relation to those in FIGS. 3 and 4.

FIG. 6 is a schematic, explanatory view in which the prosthesis is shownin place on the joint, the latter being viewed from the front. Thisfigure is purely schematic and has no other purpose but to facilitateunderstanding of the invention.

As may be seen in FIG. 1, the anterior cruciate ligament prosthesisaccording to the invention is in the form of two principal elements (1)and (2), respectively, the posteroexternal bundle (1) and theanterointernal bundle (2).

The length of these two principal elements (1, 2) ranges from 14 to 23centimeters. They each have a femoral end, (20) and (21) respectively,and a tibial end, (22) and (23) respectively, which act as ties forattaching the ligament to the femur (7) and to the tibia (8),respectively. Their typical diameter is on the order of 5 to 6centimeters, but it goes without saying that the latter can be adaptedto the morphology or activity of the recipient of the prosthesis.

Although they appear parallel in the figure, these two elements are notparallel when fastened in place within the joint. Indeed, as can be seenin FIGS. 2 and 5, when the prosthesis is in place within the joint it isslightly twisted, which is due, on one hand, to the anatomy of the jointand, on the other, to the areas of insertion made therein.

Advantageously, these bundles are in the form of multifilamentoustubular knitwear of biocompatible textile material, in particularpolyester.

These elements could, of course, be made in the form of a braid or evenmonofilamentous tubular knitwear without departing from the spirit ofthe invention.

Furthermore, in order to protect the bundles and to impart an elasticeffect thereto, they are advantageously coated with a layer ofbiocompatible polyurethane (95) at the level of their field of action inthe joint, that is to say, in the active part of the ligament, as wellas at the level of the beginning of the ends (20, 21, 22, 23) insertedin the tunnels made in the femur and in the tibia for the purpose ofattaching the ties to the femur (7) and to the tibia (8).

These two elements (1) and (2) are inserted at the level of theinsertion surfaces of the natural anterior cruciate ligament, except forthe fact that the two upper (i.e., femoral) insertions are different.They take place at the level of the posterior internal edge of theexternal condyle of the femur. The hatched area in FIG. 5 shows the siteof the femoral insertion surface of the anatomical ligament.

The lower insertion of the two elements (1) and (2) is also effected atdifferent sites at the level of the anterior prespinal surface of thetibia (8).

According to one important feature of the invention, the two principalelements (1) and (2) are made integral with each other at the level (24)of the active part of the ligament, in particular by knitting. It goeswithout saying that this could be effected by any other suitable meanssuch as braiding, welding or sewing.

Furthermore, according to another basic feature of the presentinvention, the ligament also comprises a set of intermediate elements(3, 4), also made of biocompatible textile material. Their typicaldiameter is from 2 to 3 millimeters.

These elements (3, 4) emerge directly from the principal ligaments (1,2) at the level of the intra-articular penetration areas (9, 10, 11, 12)and are actually integral with the principal elements (1, 2). Theseelements (3, 4) are crossed at the level of the active part of theligament. In other words, the intermediate ligament (3) emerging fromthe posteroexternal principal element (1) at the level of the femoralintra-articular penetration area (1) goes back into the anterointernalprincipal element (2) at the level of the tibial intra-articularpenetration area (12) Similarly, the intermediate ligament (4) emergingfrom the anterointernal principal element (2) at the level of thefemoral intra-articular area (9) goes back into the posteroexternalprincipal element (1) at the level of the tibial intra-articularpenetration area (11).

The ligament of the invention is actually made of a one-piece textilematerial. In this way, the intermediate elements are always integralwith the principal elements, particularly at the level of, and startingfrom, the femoral and tibial intra-articular penetration areas in thedirection of the exit of the insertion and attachment tunnels of theligament. Similarly, the principal elements are also integral with eachother at the level of the active part of the ligament.

In another embodiment of the present invention, the intermediateelements are also integral with the principal elements at the level of,and starting from, the femoral and tibial intra-articular penetrationareas in the direction of the exit of the insertion and attachmenttunnels without being an integral part of the principal element, but bywelding or heat sealing.

The prosthesis is attached as follows (see FIG. 6): Before anything elseand by any suitable means, femoral (6a, 6b) and tibial (6c, 6d)insertion tunnels whose respective femoral (9, 10) and tibial (11, 12)intra-articular openings are shown in FIG. 2, are hollowed out, forexample, with drill bits, in the femur (7) and in the tibia (8) at thelevel of the insertion areas of the natural ligament. Theextra-articular femoral and tibial insertion areas of the tunnels aredenoted by reference numerals 15, 16 and 17, 18, respectively, in FIG.6. When making these tunnels, the knee joint is in flexion at about60-70 degrees. The typical diameter of these tunnels (6) is from 5 to 6millimeters. The ends of the principal elements (1, 2) are inserted intothese tunnels (6) by means of the ties (20, 21, 22, 23) covered by asheath (not shown) made of polyester and provided with a needle eyeaperture to facilitate the insertion. The femoral ends (20, 21) arefirst pulled upward in order to bring into contact the interlocking area(24) of the two principal elements (1) and (2) with the femoralinsertion area (25) situated between the two tunnels (6), they are thentwisted together and, finally, are attached to the femur (7) by means ofa clip (27) commonly used for this application.

The tibial ties (22, 23) are then attached. First, the interlocking area(24) of the two principal elements (1, 2) is made flush with the area(26) situated between the two tibial intra-articular penetration areas(11, 12). Next, the ties, also covered with a rigid polyethylene sheathwith a needle eye aperture, are inserted into the corresponding tunnels(6c, 6d). Then, tension on the order of 10 kilograms is applied to theanterointernal element (2), with the knee joint being in extension,before attaching the element to the tibia by means of a clip (28).Similarly, tension of the same order is applied to the postero-externalelement (1), with the knee joint being in flexion at an angle of 30degrees, before attaching it, also by means of a clip (29), to the tibia(8).

FIGS. 3 to 5 show the ligament according to the invention in place onthe joint. In FIG. 3, only the intermediate element (3) can be seen, theother intermediate element (4) being hidden by the anterointernalelement (2). In FIG. 4, the two intermediate elements (3, 4) as well asthe two principal elements (1, 2) can be seen, with the joint incomplete extension. FIG. 5 shows only the intermediate elements (3, 4),so that their positioning within the architecture and the placement ofthe ligament according to the invention can be shown more clearly.

As indicated in the foregoing description, as a result of the variationsin the radii of curvature of the femoral condyles and the way in whichthe ligament of the invention is placed, one part of the ligament isunder tension at all times, thereby limiting or even preventing theanterior drawer movements of the tibia under the femur.

During flexion as shown in FIG. 4, as a result of the variable radii ofcurvature of the femoral condyles, the tension of the filaments makingup the prosthesis thusly constructed is gradually transmitted from theanterior part of the filaments (which are tense during extension) to theposterior part, including the crossing filaments of the intermediateelements. In other words, there is always one part of the filamentsmaking up the elements of the prosthesis which is under tension.

Similarly, during rotation, the two bundles in internal rotation willhave a tendency to tighten along their axes, thus reducing the distancebetween the femoral condyles and the glenoid cavity, causing acoaptation of the articular surfaces.

In external rotation, the two principal elements (1) and (2) will have atendency to relax and, as a result of their direction, the intermediateelements will limit the tendency toward anterior drawing movements andthe tendency toward external rotation.

Thus, at every degree of flexion, this geometrical arrangement makes itpossible for a group of fibers to tighten, and the area under tensionwith this arrangement varies during flexion.

Furthermore, when there are excessive stresses, such as during athleticactivities, that is to say, when there is a greater tendency towardanterior drawer movements, a greater quantity of fibers making up thedifferent elements of the ligament of the invention is brought into playto resist and work against these anterior drawer movements. This featureis inherent in the interlocking of different bundles, which increasesthe mechanical strength of the ligament.

Thus, the present invention offers a number of advantages heretofore notprovided by cruciate ligament prostheses, particularly the greatereffectiveness of the ligament in controlling the anterior drawermovements and articular coaptation, which absolutely could not beachieved with single-bundle ligaments or with multiligament prostheses.

We claim:
 1. A biocompatible synthetic ligament replacement of naturalligaments at the intra-articular area between femoral and tibial bonesof a knee joint, including an elongated element terminating at oppositefirst and second ends, each element comprising:first inactive end tiesconfigured to be inserted into first tunnels bored in the femur; secondinactive end ties configured to be inserted into second tunnels bored inthe tibia, wherein said first ties are attached to the femur and extendtherefrom to the intra-articular area through said first tunnels, andsaid second ties are attached to the tibia and extend therefrom to theintra-articular area through said second tunnels; and an activemidportion intermediate said ends to be positioned in theintra-articular area of the knee joint, comprising:(a) first and secondsubstantially parallel principal elements integral at one end to saidfirst ties and at an opposite end to said seconds ties, said principalelements having means for integral connection to each other; and (b) apair of intermediate crossed elements which are freely crossed so as tointegrally connect said first principal element to said second principalelement, respectively, thereby distributing a load on one of saidprincipal elements at one end thereof to both of said principal elementsat the other end thereof.
 2. The synthetic ligament of claim 1, whereinsaid principal elements and said intermediate elements are made of abiocompatible textile material, and wherein said intermediate elementsare connected to said principal elements in the vicinity ofintra-articular femoral and tibial penetration areas of said tunnels. 3.The synthetic ligament of claim 1, wherein said integral connection ofsaid principal elements has a construction selected from the groupconsisting of braiding, knitting, welding and sewing.
 4. The syntheticligament of claim 1, wherein said intermediate elements are connected tosaid principal elements by heat sealing.
 5. The synthetic ligament ofclaim 1, wherein ends of said first ties and said second ties which areattached to the femur and tibia, respectively, include a polyethylenesheath and are provided with a needle eye aperture to enable passage ofsaid ends through said first tunnels and said second tunnels.
 6. Thesynthetic ligament of claim 1, wherein said principal elements and saidintermediate elements are made of a one-piece knitted fabric ofmultifilament yarn selected from the group consisting of polyester,propylene and glass yarns.